1. Field of the Invention
The present invention relates to a toroidal-type continuously variable transmission which can be used, for example, as a transmission unit for a transmission of a vehicle or as a transmission for various industrial machines.
2. Description of the Related Art
Conventionally, use of such a toroidal-type continuously variable transmission as shown in FIGS. 5 and 6 as a transmission of a vehicle has been studied and used in some sectors of the vehicle industry. In this toroidal-type continuously variable transmission, for example, as disclosed in JP-62-714650, an input side disk 2 is supported concentrically with an input shaft 1 and an output side disk 4 is fixed to the end portion of an output shaft 3 which is disposed concentrically with the input shaft 1. In the interior of a casing 5 (see FIG. 8 which will be discussed later) in which a toroidal-type continuously variable transmission is stored, there are disposed trunnions 7, 7 respectively swingable about their associated pivot shafts 6, 6 which are disposed at positions respectively twisted with respect to the input shaft 1 and output shaft 3.
On each of the trunnions 7, 7, there are disposed a pair of units (two units) of the above-mentioned pivot shafts 6; more specifically, the pair of pivot shafts 6 are disposed on the outer surfaces of the two end portions of each trunnion 7 in such a manner that the two pivot shafts 6, 6 are concentric with each other. The center axes of these pivot shafts 6, 6 are present at twisted positions which do not cross with the center axes of the disks 2, 4 but extend in a direction at right angles or substantially right angles with respect to the direction of the center axes of the disks 2, 4. Also, the base half sections of displacement shafts 8, 8 are supported on the central portions of the trunnions 7, 7 and thus, by swinging the trunnions 7, 7 about the pivot shafts 6, 6, the inclination angles of the displacement shafts 8, 8 can be adjusted freely. On the peripheries of the front half sections of the displacement shafts 8, 8 which are respectively supported on their associated trunnions 7, 7, there are rotatably supported power rollers 9, 9, respectively. And, the power rollers 9, 9 are held by and between the respective inner surfaces 2a, 4a of the input side and output side disks 2, 4.
The section of each of the mutually opposing inner surfaces 2a, 4a of the input side and output side disks 2, 4 has an arc-shaped concave surface which can be obtained by rotating an arc with the pivot shaft 6 as the center thereof or by rotating a curved line which is approximate to such arc. And, the peripheral surfaces 9a, 9a (each of which is formed as a spherically convex surface) of the power rollers 9, 9 are respectively contacted with the inner surfaces 2a, 4a of the input side and output side disks 2, 4. Also, between the input shaft 1 and input side disk 2, there is interposed a loading cam device 10, and the loading cam device 10 presses the input side disk 2 elastically toward the output side disk 4, to thereby drive or rotate the input side disk 2 freely.
When the above-structured toroidal-type continuously variable transmission is in use, as the input shaft 1 is rotated, the loading cam device 10 rotates the input side disk 2 while pressing it against the plurality of power rollers 9, 9. And, the rotation of the input side disk 2 is transmitted through the plurality of power rollers 9, 9 to the output side disk 4, thereby rotating the output shaft 3 which is fixed to the output side disk 4.
Now, description will be given below of a case where the rotation speeds of the input shaft 1 and output shaft 3 are changed. First, in case where deceleration is made between the input shaft 1 and output shaft 3, the trunnions 7, 7 are respectively swung about their associated pivot shafts 6, 6 to thereby incline the displacement shafts 6, 8 in such a manner that the peripheral surfaces 9a, 9a of the power rollers 9, 9, as shown in FIG. 5, are respectively contacted with the near-center portion of the inner surface 2a of the input side disk 2 and with the near-outer-periphery portion of the inner surface 4a of the output side disk 4.
On the other hand, in the case of acceleration, the trunnions 7, 7 are respectively swung about their associated pivot shafts 6, 6 to thereby incline the displacement shafts 8, 8 in such a manner that the peripheral surfaces 9a, 9a of the power rollers 9, 9, as shown in FIG. 6, are respectively contacted with the near-outer-periphery portion of the inner surface 2a of the input side disk 2 and with the near-center portion of the inner surface 4a of the output side disk 4. By the way, in case where the inclination angles of the displacement shafts 8, 8 are set in the intermediate between those shown in FIGS. 5 and 6, there can be obtained an intermediate gear change ratio between the input shaft 1 and output shaft 3.
Further, FIGS. 7 and 8 respectively show a further specific version of a toroidal-type continuously variable transmission which is disclosed in U.S. Pat. No. 4,955,246. Specifically, in this toroidal-type continuously variable transmission, an input side disk 2 and an output side disk 4 are rotatably supported on the periphery of a cylindrical-shaped input shaft 11, respectively. Also, between the input side disk 2 and the end portion of the input shaft 11, there is interposed a loading cam device 10. On the other hand, to the output side disk 4, there is connected an output gear 12 in such a manner that the output side disk 4 and output gear 12 can be rotated in synchronization with each other.
In the toroidal-type continuously variable transmission, there are disposed a pair of trunnions 7, 7. On the two end portions of each trunnion 7, there are disposed pivot shafts 6, 6 which are concentric with each other. The pivot shafts 6, 6 are respectively supported on a pair of support plates 13, 13 serving as support members in such a manner that they can be swung and can be shifted in the axial direction thereof (in FIG. 7, in the front and back direction; and, in FIG. 8, in the right and left direction). And, the base half sections of displacement shafts 8, 8 are supported on the intermediate portions of the trunnions 7, 7. These displacement shafts 8, 8 are structured such that the base half sections and front half sections thereof are eccentric with respect to each other. Also, the base half sections of the displacement shafts 8, 8 are rotatably supported on the intermediate portions of the trunnions 7, 7, while power rollers 9, 9 are rotatably supported on the front half sections of the displacement shafts 8, 8, respectively.
By the way, the pair of displacement shafts 8, 8 are disposed at positions just 180xc2x0 opposite to each other with the input shaft 11 between them. Also, the direction in which the base half sections and front half sections of the displacement shafts 8, 8 are eccentric with each other is set as the same direction (in FIG. 8, the reversed right-and-left direction) with respect to the rotation direction of the input side and output side disks 2, 4. Further, this eccentric direction is a direction which extends substantially at right angles to a direction where the input shaft 11 is disposed. Therefore, the power rollers 9, 9 are supported in such a manner that they can be shifted slightly with respect to the direction where the input shaft 11 is disposed.
Also, between the outer surfaces of the power rollers 9, 9 and the inner surfaces of the intermediate portions of the trunnions 7, 7, there are interposed thrust ball bearings 14, 14 and thrust needle roller bearings 15, 15 sequentially in order starting from the outer surfaces of the power rollers 9, 9. The thrust ball bearings 14, 14, while supporting thrust-direction loads applied to the power rollers 9, 9, allow the power rollers 9, 9 to rotate, Also, the thrust needle roller bearings 15, 15, while supporting thrust loads applied from the power rollers 9, 9 to outer races 16, 16 forming the thrust ball bearings 14, 14, allow the front half sections of the displacement shafts 8, 8 and the outer races 16, 16 to swing about the base half sections of the displacement shafts 8, 8. Further, the trunnions 7, 7 are structured such that they can be shifted in the axial directions of the pivot shafts 6, 6 by their associated actuators 17, 17 of an oil-pressure type.
In the case of the above-structured toroidal-type continuously variable transmission, the rotation of the input shaft 11 is transmitted through the loading cam device 10 to the input side disk 2. And, the rotation of the input side disk 2 is transmitted through the pair of power rollers 9, 9 to the output side disk 4 and, further, the rotation of the output side disk 4 is taken out from the output gear 12.
To change the rotation speed ratio between the input shaft 11 and output gear 12, using the actuators 17, 17, the pair of trunnions 7, 7 may be shifted respectively in their mutually opposite directions; for example, the power roller 9 disposed in the lower stage in FIG. 8 may be shifted right in FIG. 8, whereas the power roller 9 disposed in the upper stage in FIG. 8 may be shifted left in FIG. 8. This changes the direction of tangential-direction forces to be applied to the contact portions between the peripheral surfaces 9a, 9a of the power rollers 9, 9 and the inner surfaces 2a, 4a of the input side and output side disks 2, 4. With such change of the direction of the forces, the trunnions 7, 7 are swung in the mutually opposite directions about their respective pivot shafts 6, 6 which are pivotally supported on the support plates 13, 13. As a result of this, as shown in FIGS. 5 and 6, the contact positions between the peripheral surfaces 9a, 9a of the power rollers 9, 9 and the inner surfaces 2a, 4a of the input side and output side disks 2, 4 are shifted, thereby changing the rotation speed ratio between the input shaft 11 and output gear 12.
When power is transmitted by the toroidal-type continuously variable transmission, the power rollers 9, 9 are shifted in the axial direction of the input shaft 11 due to the elastic deformation of the component parts of the toroidal-type continuously variable transmission. And, the displacement shafts 8, 8, which support the power rollers 9, 9, are slightly rotated with their respective base half sections as the rotation centers thereof. As a result of this slight rotation, the outer surfaces of the outer races 16, 16 of the thrust ball bearings 14, 14 and the inner surfaces of the trunnions 7, 7 are shifted with respect to each other. Between these outer and inner surfaces, there are present the thrust needle roller bearings 15, 15 and, therefore, the relative shift of the outer and inner surfaces requires a small force.
In the case of the toroidal-type continuously variable transmission providing the above-mentioned structure and operation, power transmission between the input shaft 11 and output gear 12 is carried out by the two power rollers 9, 9. Therefore, a force per unit area, which is transmitted between the peripheral surfaces 9a, 9a of the power rollers 9, 9 and the inner surfaces 2a, 4a of the input aide and output side disks 2, 4, is large; and, the limit of the power that can be transmitted is relatively low. In view of such circumstances, conventionally, there has been proposed an idea that, in order to be able to increase the power that can be transmitted by a toroidal-type continuously variable transmission, the number of power rollers 9, 9 is increased.
Conventionally, as a structure for increasing the number of power rollers 9, 9 for this purpose, there is known a structure in which, for example, as disclosed in U.S. Pat. No. 5,048,359, between a set of input side and output side disks 2 and 4, there are interposed three power rollers 9, 9 and transmission of power is carried out by these three rollers 9, 9. In the case of the structure disclosed in the cited patent, as shown in FIG. 9, at three positions of a fixed frame 18 which are spaced at equal distances from each other in the circumferential direction of the fixed frame 18, there are pivotally supported the respective intermediate portions of three 120xc2x0xe2x80x94curved support pieces 19, 19 which respectively serve as support members. And, between the mutually adjoining support pieces 19, 19, there are supported their respective trunnions 7, 7 in such a manner that they can be swung as well as can be shifted in the axial direction thereof.
The respective trunnions 7, 7 can be freely shifted by their associated actuators 17, 17, of the oil-pressure type in the axial direction of pivot shafts 6 which are disposed on the two end portions of each of the trunnions 7, 7 in such a manner that they are concentric with each other. Oil pressure cylinders 20, 20, which respectively form their associated actuators 17, 17, are in communication through a control valve 21 with the discharge port of a pump 22 serving as an oil pressure source. The control valve 21 includes a sleeve 23 and a spool 24 which can be respectively shifted in the axial direction thereof (in FIG. 9, in the right and left direction). By the way, as the actuators 17, 17, there are used actuators each of a double-acting type which can generate a force in both ways of the axial direction thereof by switching the pressure oil supply and drain directions over each other.
To change the inclination angles of the power rollers 9, 9 pivotally supported on their respective trunnions 7, 7 by their respective displacement shafts 8, 8, the sleeve 23 may be shifted in the axial direction thereof (in FIG. 9, in the right and left direction), using a control motor 25. As a result of this, the pressure oil discharged from the pump 22 is fed into the respective oil pressure cylinders 20, 20 through an oil pressure pipe. And, drive pistons 26, 26, which are respectively fitted with their associated oil pressure cylinders 20, 20 and are used to shift the trunnions 7, 7 in the axial direction of their associated pivot shafts 6, 6, are caused to shift in the same direction with respect to the rotation direction of the input side and output side disks 2 and 4 (see FIGS. 5 and 6). And, similarly to the structure shown in FIGS. 7 and 8, with such shift of the drive pistons 26, 26, the trunnions 7, 7 are shifted in the axial direction of their respective pivot shafts and are swung about the pivot shafts. Also, operation oil, which is pushed out from the oil pressure cylinders 20, 20 with the shifting movements of the respective drive pistons 26, 26, is also returned to an oil basin 27 through the oil pressure pipe (a portion of which is not shown) including the control valve 21.
On the other hand, the shifting movements of the drive pistons 26 caused by the above feed of the pressure oil into the oil pressure cylinders 20 as well as the shifting movements of the trunnions 7 connected to the drive pistons 26 are transmitted to the spool 24 through precess cams 28 and links 29, thereby causing the spool 24 to shift in the axial direction thereof. As a result of this, in a state where the drive pistons 26 are shifted by a given amount, the flow passage of the control valve 21 is closed to thereby stop the supply of the pressure oil to the respective oil pressure cylinders 20, 20. Therefore, the shifting amounts of the respective trunnions 7, 7 in the axial direction thereof correspond to the shifting amount of the sleeve 23 caused by the control motor 25,
In the case of the conventional toroidal-type continuously variable transmission having the above-mentioned structure and providing the above-mentioned operation, the installation space of the actuators 17, 17 is large, which increases the size of the toroidal-type continuously variable transmission. On the other hand, in JP-A-7-2599470 there is disclosed a structure in which, as shown in FIG. 10, three trunnions 7, 7 are connected in series to one another by two link mechanisms 30, 30 and these three trunnions 7, 7 can be shifted using a single actuator 17 which is a double-acting oil pressure actuator. Also, in JP-A-11-303963, there is disclosed a structure in which, as shown in FIG. 11, support pieces 19a, 19a are supported swingably and shiftably and, using these support pieces 19a, 19a, the movements of trunnions 7, 7 mutually adjoining in the circumferential direction of the structure can be transmitted to each other. In the case of the structure shown in FIG. 11 as well, driving actuators 17, 17 are freely able to press against the end faces of pivot shafts 6, 6 respectively disposed on the circumferential-direction two end portions of their associated trunnions 7, 7 in the axial directions of the pivot shafts 6, 6.
In the case of the conventional structures respectively shown in FIGS. 10 and 11, the installation space of the actuators 17 can be reduced to thereby be able to reduce the size and weight of the structures; however, to be able to restrict the shifting amounts of all of the trunnions 7, 7 severely, the movable parts of the structures must be formed very precisely, which results in the high manufacturing cost. In other words, in the toroidal-type continuously variable transmission, depending on the size thereof, there is a possibility that, in case where the trunnions 7, 7 are respectively shifted only by an amount of the order of 0.1 mm in the axial directions of their associated pivot shafts 6, 6, the toroidal-type continuously variable transmission can start its gear change operation. Therefore, in case where the shifting amounts of the respective trunnions 7, 7 are different on the order of 0.1 mm from each other, there arises a possibility that the inclination angles of the trunnions 7, 7 about their respective pivot shafts 6, 6 can differ from each other to thereby lower greatly the power transmission efficiency and durability of the toroidal-type continuously variable transmission.
That is, when enforcing the structures respectively shown in FIGS. 10 and 11, the rickety movements of the respective movable parts thereof must be minimized as much as possible to thereby synchronize the shifting movements of the three trunnions 7, 7 with each other at a difference level sufficiently lower than the level of the shifting amount of 0.1 mm (that is, with a sufficiently higher precision). Here, in order that the shifting movements of the respective movable parts can be carried out smoothly as well as the rickety movements thereof can be minimized as much as possible, the dimensional precision and shape precision of the respective components of the toroidal-type continuously variable transmission must be enhanced greatly, which makes it troublesome to work the respective components, resulting in the increased manufacturing costs of the respective components and thus the increased cost of the toroidal-type continuously variable transmission. Further, as shown in FIGS. 10 and 11, in case where the three trunnions 7, 7 are connected together in series in the shifting direction thereof and the actuators 17, 17 are disposed only on the connecting-direction end portions of trunnions 7, 7, the elastic deformation of parts including the trunnions 7, 7, which are used to transmit the shifting movements of the trunnions 7, 7, must also be taken into consideration. It is very difficult to synchronize the shifting movements of the trunnions 7, 7 with each other at a severe level (that is, at a shifting amount level sufficiently smaller than the shifting amount of 0.1 mm).
The present invention aims at eliminating the drawbacks found in the above-mentioned conventional toroidal-type continuously variable transmissions. Accordingly, it is an object of the invention to provide a toroidal-type continuously variable transmission which can be reduced in the size and weight thereof.
In attaining the above object, according to a first aspect of the invention, there is provided a toroidal-type continuously variable transmission, including: a casing; an input shaft rotatably supported within the casing; an input side disk supported on the periphery of the input shaft in such a manner as to be rotatable together with the input shaft; an output side disk disposed so as to be concentric with the input side disk and to be relatively rotatable with respect to the input side disk; trunnions interposed between the input side and output side disks in such a manner as to be respectively swung about pivot shafts disposed at twisted positions with respect to center axes of the two disks, the trunnions including three first, second and third trunnions for each pair of input side and output side disks; displacement shafts provided on the respective trunnions so as to project from the inner surfaces of the trunnions, the one displacement shaft being provided for each trunnion: power rollers rotatably supported on the respective displacement shafts and interposed between the input side and output side disks, the one power roller being provided for each trunnion; and, actuators for shifting the respective trunnions in the axial direction of the pivot shafts disposed on the two end portions of the trunnions. The actuators are composed of a pair of first oil pressure actuators of a single acting type for shifting the first trunnion in the mutually opposite directions through link arms, and second and third oil pressure actuators of a double acting type respectively disposed on the second and third trunnions.
Further, according to a second aspect of the invention, in the toroidal-type continuously variable transmission as set forth in the first aspect, supply and drain of pressure oil to and from the first to third oil pressure actuators are carried out in synchronization with one another using a single control valve.
Moreover, according to a third aspect of the invention, in the toroidal-type continuously variable transmission as set forth in the first aspect, the first oil pressure actuator includes a rod butting against one side surface of a base end portion of the link arm at a leading end face of the rod, and a portion of the base end portion of the link arm, which is to be butted against the leading end face of the rod, is formed as a partially cylindrical-shaped convexly curved surface.
In addition, according to a fourth aspect of the invention, in the toroidal-type continuously variable transmission as set forth in the first aspect, one-side surfaces of leading end portions of the link arms are respectively engaged with end portions of the pivot shafts respectively disposed on two end portions of the first trunnions, thrust needle roller bearings are respectively interposed between the one-side surfaces of the leading end portions of the link arms and the end portions of the pivot shafts, and each of the thrust needle roller bearings includes a pair of races, and one of the races, which is disposed on the link arm side, has a surface to be contacted with a leading end portion side surface of the link arm formed as a spherically convex surface or as a conically convex surface.
Further, according to a fifth aspect of the invention, in the toroidal-type continuously variable transmission as set forth in the first aspect, one-side surfaces of leading end portions of the link arms are respectively engaged with end portions of the pivot shafts respectively disposed on two end portions of the first trunnions, and the leading end portion of the link arm has a cylindrically projecting portion being loosely inserted into a circular hole formed in a central portion of the pivot shaft.
In the above-structured toroidal-type continuously variable transmission according to the invention, not only the installation space for the actuators used to shift the respective trunnions is reduced to thereby be able to reduce the size and weight of the toroidal-type continuously variable transmission but also the shift amounts of the respective trunnions are restricted severely to thereby be able to realize an accurate shifting operation. Also, even in case where the shape precision and dimension precision of the component parts of the toroidal-type continuously variable transmission are not enhanced extremely, the shift amounts of the respective trunnions can be restricted severely. Further, since an actuator is provided for each of the trunnions, there is eliminated a possibility that there can occur an error due to the elastic deformation of the shift transmitting parts including the trunnions caused by their shift transmission movements, which can also contribute toward restricting the shift amounts of the trunnions severely. Thanks to the above, the transmission efficiency and durability of the toroidal-type continuously variable transmission, in which three power rollers are interposed between a pair of input side and output side disks, can be sufficiently secured while being able to reduce the size and weight of the toroidal-type continuously variable transmission.